The present invention relates to photography.
In particular, the present invention relates to devices such as cameras and exposure meters.
As is well known, devices of the above type operate in accordance with variable factors one of which is the intensity of light at a subject which is to be photographed. These devices have photoelectric converters to be used for controlling the operation of the shutter of a camera, for example. For this purpose photoelectric conversion information is obtained by utilizing a semiconductor element under conditions where a constant voltage is applied thereto so that there will be a resulting resistance corresponding to the intensity of light received by the semiconductor. With such an arrangement the photoelectric conversion information is obtained in the form of a voltage difference which develops across a predetermined resistor when an electric current flows through the resistor which is situated in an electrical circuit including either a single semiconductor element or a series of parallel circuit portions having therein a single semiconductor element and a resistor having a preselected suitable resistance. In conventional circuits of this type the semiconductor element has a photoelectric characteristic and is used as a passive element.
As a result, conventional circuits of the above type require a power source in order to obtain a photoelectric conversion. Such conventional circuitry has a low photoelectric conversion efficiency as a result of the power consumed by the resistor or resistors included in the circuit.
Accordingly, it is difficult to carry out photometric operations for a subject which has a low luminance. In addition there is a danger that the accuracy of the circuit calculation operations and the timing circuit operation for determining the exposure time, depending upon the photoelectric conversion output, is lowered as the power voltage is lowered.